Response of native marine sponges to invasive Tubastraea corals: a case study

Despite the massive expansion of the invasive corals Tubastraea spp. in the Tropical Western Atlantic, some sponge species may outcompete them on a local scale. The aims of the present study were: (1) to describe the spatiotemporal dynamics of the benthic community and (2) to assess the interactions between marine sponges and invasive Tubastraea corals. Communities were monitored at four locations and four times (2013–2015) in Ilha Grande Bay, southeastern Brazil. The percent cover of the dominant taxa in the benthic communities was calculated and all interactions among native sponges and Tubastraea spp. corals counted within photoquadrats. These in situ observations were used to assess four categories of interaction types. We did not find statistical differences in the benthic communities among locations and times. Turf forming algae and Palythoa caribaeorum represented 60–70% of the benthic community. The number and types of interactions between sponges and corals differed significantly among locations. The most common interaction was contact without dominance. Iotrochota arenosa and Scopalina ruetzleri were the most common sponge species competing with Tubastraea spp. Furthermore, Desmapsamma anchorata and I. arenosa were the main sponge species able to occasionally kill the invasive corals by overgrowth. However, the slow rate of overgrowth by sponges was not able to prevent the fast expansion of the non-indigenous corals. Hence, population studies on native and alien species may help predict the effects of biological invasion on local biodiversity.